I Should Have Known Better
by Zuzzeroo
Summary: Derek and Casey come home from University for a visit, and realize a week without touching is a lot longer than it seems. Dasey. R&R!


_Okay, so it's been a while since I updated my "Believe It Or Not" story and I'm working on that now. I have a few more big exams to go for this year and I am done for the summer, which means lots of car trips, which means I bring my laptop and write. A lot. So be ready for a whole ton of one-shots and new stories from me! _

_This is some weird idea I've had floating around for a while and decided I might as well post it. Please let me know what you think and if you find any big errors, let me know._

_R&R!_

_Disclaimer: I own nothing, although a plate of chocolate chip pancakes now would be nice._

* * *

_Day One, Friday_

"Casey!" Derek dodged the arms of his step-mom and slipped over to the living room, dropping the bags he was carrying unceremoniously at Casey's feet.

"Der-ek!" She screeched at the same time as Nora clicked her tongue at him.

He rolled his eyes, throwing in a quick line as he made his way over to his old faithful friend. "Can you grab those? Thanks babe." And then he sat down dramatically in the recliner, still perched in its old spot next to the couch, though that old piece of furniture finally been replaced with a newer model when Susie got baby puke on it last fall.

Casey rolled her eyes, her arms still wrapped around her Mother's waist.

"He's usually better at home. I guess I haven't taken him out enough recently."

Nora laughed. "I don't think it's ever going to change between you two. Dating has just made it a whole lot grosser, when you two make up."

Casey blushed and Derek winked at his red girlfriend, grabbing the remote off the stand beside him.

"Is there any food in this house, Nora?"

Nora opened her mouth to respond but her eldest raised up her hand. "Don't answer him Mom. He's totally capable of getting his own food."

Derek scoffed. "That's not very nice. If she honestly wants to get me food, Case, why tell her not to?"

Both women just rolled their eyes at him before Nora turned back to her daughter.

"I hope you don't mind but I was just about to go pick up the rest of the kids from school. Susie's napping right now and she should be out for a good hour or so. There _is _leftover meatloaf from last night that you can heat up if you're hungry and don't feel bad about wandering around; this is still your home now as much as it was before and...I'm just so glad you're home again." She gushed.

After a few more hugs from Casey and even a small one from Derek, Nora left the house to go pick up the kids, leaving Derek and Casey alone with their little, sleeping sister upstairs.

The hockey game on was long and boring and Casey felt her brain practically begging her to do something more productive with it. The second period was just starting when her stomach began to rumble.

Trying to ignore it, Casey stretched out on the couch, letting her heeled feet dangle off the edge. She glanced back at Derek, who seemed so enthralled in the hockey game, that he didn't even mention the fact that she was staring at him, or that they were by themselves, which was going to be very difficult now that they were home, spending the whole week with their families.

With a sigh, she stood up, announcing that she was going to the kitchen, though she doubted he really heard her, for all she got was a nod in her general direction, which meant nothing.

The meatloaf was sitting on a pan waiting to go in the oven as soon as it was the right temperature when she felt arms slip around her waist and Derek's chin perched on her shoulder.

"Mmmm, how did you know I was hungry?"

His hands were slowly caressing her sides, up and down, which was one of her most tickles spots and she squirmed in his grasp, trying to get away from him.

"It's for me, not you."

"Mmhmm." He moved her hair out of the way and she felt his lips land lightly on her neck. Casey's eyes slowly slide shut as her head tilted to the side, giving him more access. His lips dragged themselves across her neck and she felt her skin tingle and that warm feeling settle in her stomach. Shaking her head she forced her eyes open and stood up straight, pulling away from him.

He was pouting; she could feel it, even if he was behind her and she couldn't see.

"You're no fun anymore."

She laughed. "Was I no fun when I let you pull over on the side of the highway before we got here and let you drag me to the back seat? Besides, I thought we agreed that while we were at our parent's house, we wouldn't do anything like this?"

Derek snorted. "You agreed. I personally don't think I can wait a week without touching you."

Casey laughed when he frowned, reaching up to playfully pinch his cheeks.

"Poor little Derek."

He swatted her hand away from his face, but caught it with his own, pulling her flush up against him.

"I don't think you want to wait a week either." His face was getting closer to her own and his warm breath on her lips was dragging her eye lids back down, her mouth opened in anticipation and she sighed at the comforting, rush of a feeling as his lips lightly touched her own.

_BAM!_

"SMEREK!"

The hyper preteen darted into the kitchen, past Lizzie who was carrying a bag full of groceries with a smirk on her face which was obviously there due to the affections she had just seen her older siblings show.

Marti pushed past Casey, grabbing her older brother's hand and tugging on it, a big grin on her face. "I missed you!" Derek bent down to pick her up, pretending to buckle under her weight. "You've gotten a lot bigger Smarts. It's been what? Two months since I last saw you?"

Marti giggled, throwing her arms around his neck. Then she seemed to notice Casey standing there, very close to Derek with one of her hands still resting on his hip. The little girl looked at it pointedly until Casey noticed and moved it, blushing in the process and became very interested in putting the meatloaf in the oven.

"I missed you too Casey, don't worry. Just not as much as Derek."

Casey forced a smile at the little girl, trying to ignore her sniggering boyfriend. "That's okay Marti. I missed you too."

_Day Two, Saturday_

Waking up bright and early to the smells of eggs and bacon was something Derek wished would happen every morning. Especially when the smell of chocolate chip pancakes was blended in. But waking up bright and early, rolling over with your arm outstretched, blindly trying to find the one person who has been sleeping to the right of you for as long as you can remember, the one person who you don't mind to see first thing in the morning. But only to have your arm fall down on the empty mattress is a reminder that the next few days are going to be long and miserable when your bed buddy is sleeping by herself in another room upstairs.

Yawning and burying his head in the pillows, Derek tried to pretend that it was actually 10:30am and not 7:00am and that he was back home in his apartment, getting ready to have one of his famous breakfast specialties, toast and peanut butter, and watch Casey do her morning yoga on the balcony of their apartment.

Somewhere upstairs, a baby started wailing and he rolled out of bed, colliding with the carpet with a solid thud.

Good morning, good morning.

The kitchen was filled with hectic, busy noise and Derek felt like he was back in high school, waking up with a massive hangover from Friday's party and trying to put on a positive, happy smile for his family under Nora's disproving glance and Casey's knowing huff as she banged and clattered as many pots and pans as she could as she cleaned up, making sure he heard all of them and grinned at his discomfort.

Now, it was very much the same, though his hangover was mainly from the tiredness he felt. It's odd how you suddenly can't sleep very well when you get all the room in a bed.

"Morning Derek." Nora chirped, her face bright and smiley as she brushed her bangs out of her eyes with her elbow; hand grasping a spoon filled with baby gunk and poising it in front of little Susie's mouth as she fussed and tried to bat it away with her little hands.

Everyone else was already in the dining room, mouths full of hash browns and toast as they laughed and talked amongst themselves. He stumbled in.

"So the dead do rise." Edwin commented and Derek resisted the urge to flip him off in front of Marti who was happily pilling her eggs together on the side of her plate. Casey grinned at his pained expression and patted the empty chair next to her.

As soon as he hit the chair, she was handing him a mug filled with coffee, cream no sugar and he felt his heart swell and before he knew what he was doing, he leaned over and kissed her lightly on the corner of the mouth.

They both froze and his eyes slowly moved from Casey's too Edwin's, Lizzie's and Marti's but it looked as if they hadn't even noticed. Lizzie and Edwin were back in their own little conversation and Marti seemed to be making some leaning tower of eggs.

Derek looked back at Casey, giving her a weak smile and leaned in again, kissing her properly on the lips. It wasn't a long kiss or anywhere near as bad as it could have been but Nora shrieked from somewhere behind him and he frowned as Casey pulled back.

His step-mom was standing there; Susie balanced on her hip and a plate of pancakes in her hand.

"Sorry," His step-mom said hesitantly, lowering Susie down into her highchair. "I didn't mean to do that, it was just startling."

He watched as Casey gave her Mom a shaky smile. "It's alright. It won't happen again. I know how wonderful you've been about Derek and I as a couple and I don't want to ruin any of that. Don't worry, Mom."

Nora nodded and placed the pancakes on the table before making her way upstairs, to where her and George's bedroom now was, to be closer to the baby's. Derek stared at his girlfriend feeling a whole lot worse than when he was battling a hangover. They had decided no PDA around the family, but he actually felt it now hearing her say it.

Casey looked back at him, but her expression was unreadable which was confusing him even more. Then Edwin reached across the table, grabbing four of the large flapjacks and plopping them on his plate. Lizzie reached across the table, grabbing the last one before anyone else could and her arm bumped Marti's plate, bringing the egg architecture crashing down.

The moment was lost.

_Day Three, Sunday_

Sunday afternoon's were always filled with roast chicken and, now that it was summer, water fights. In the winter it was pillow fights and once an ice cream cake fight, but Nora had ended that fairly quickly, and after two hours of scrubbing every inch of the cupboards and floors in the kitchen, it took Derek a while to ever look at strawberry ice cream again without thinking of soap.

Now he was armed with a waterproof walkie-talkie and camouflage gear. There was some sort of branch poking him in an unpleasant spot where he crouched behind a bush and the sun and sweat were sticking his shirt to his back.

A mosquito was buzzing around his head and he was just about to reach up and swat it away when a small hand grasped his arm.

"Don't! You'll give away our position."

He rolled his eyes and looked down at Casey. She had her hair pulled back out of her face yet some strands had managed to escape and Derek lightly brushed a few back. Casey scowled at him and knocked his hand down again.

"Are you _trying_ to get us soaked?"

Derek winked at her and smirked when she smacked his shoulder with a huff.

"Don't be so disgusting. Not everyone thinks like that, you know."

"You do occasionally."

"No."

"Yes. Remember that time when we Ed and Lizzie came to visit and we took them to _Boston Pizza_? With the straws and chilli powder?" Derek chucked at the memory. "And you said-"

"Shhhh!" Casey hissed at him, peeking out from between the branches and leaves. "It's quiet. Marti was out poking around the bike shed a minute ago, now she's gone."

Derek stared at her incredulously. "Marti has been twenty feet away from us this whole time and you never thought to even mention it at all?"

Casey shrugged. "You were talking dear, I didn't want to interrupt."

"That's so bullshit."

"It is what it is." Came a voice from somewhere off to Derek's left. He winced and turned away from his smirking girlfriend to glance upwards at his little sister, a bright orange super soaker in her hands, aimed straight for his chest.

"Smarti," Derek held up his hands in surrender, smiling. "You know you don't want to do this."

Marti just glared at him, long and hard until Casey finally cleared her throat, stood up and brushed off her jeans. "I'm going to head inside and get a drink."

And as soon as the back door slammed shut, Marti was on him like lightning.

Damn Casey.

_Day Four, Monday_

"Okay, it says we need bread, olives, orange juice, baby-crackers for Susie, nacho chips and band-aids." Casey said as she read the grocery list.

Derek rolled his eyes, grabbing the closest cart, placing his year and a half year old baby sister in it. "Is that everything Dad told you to get?"

Casey shook her head.

"There's still the list that Mom wants us to get, which is at least tripe the size of this one."

"Great."

They had cruised around the aisles for a good forty five minutes, collecting all of the odd items their parents had requested. Neither of them were really big fans of grocery shopping, unless Casey had a solid week to plan ahead, gather all the coupons and sort them into alphabetical order and arrange the fliers by expiration date.

But when you're home for a week and have been stuck inside a house with a brother who still hasn't passed his phase on "human gas research", it's nice to get out of the house for a little while. Even if it does involve you bringing along your girlfriend and your little half sister.

Derek leaned back impatiently on one of the shelves full of diapers for children and old people and watched as Casey scanned the boxes of band-aids lining the shelf across from him. She read the back of each one, comparing the waterproof ones to the _Dora The Explorer _kind.

Susie was sitting in the little seat, kicking her legs and plucking at the hair on her Barbie dolls head, that she was clutching tightly in her little fist.

Neither of them were capturing his interest at the moment.

His eyes wandered down the aisle to a small display to his right. His feet headed over in that direction and he found himself glancing back over his shoulder, checking on the girls. Casey had placed the waterproof box back on the shelf and was reaching for a box with regular, brown band-aids on it. Susie's doll was now pretty much bald, the blonde hair fluttering to the shiny, waxed supermarket floor. They wouldn't even notice that he moved away from the cart.

This was too easy.

The condom display was way more interesting than band-aid shopping. He couldn't remember if he had brought any on the trip with him. He usually left a few in his wallet, but last week's camping trip had taken care of those.

Casey had told him very strongly, back at their apartment, that they would _not_ be having sex or take part in any sort of sexual activities while they were sleeping under their parent's roof with their siblings right next door and across the hallway.

But, he had a feeling that she was getting a little anxious as well. His brow furrowed as he look at the different kinds...flavoured? Ribbed? It was still going to take some convincing, he decided, to get her to go back on her "No Sex For A Week" rule.

Finally he just grabbed both, and walked slowly back to the cart and tossed them in, pulling a bag of chips over top of them.

They were at the till, the cashiers name was Hannah and she was smiling at them, or him, flicking her strawberry blonde hair back over her shoulder.

Casey huffed, annoyed, and began to unload the items in their cart onto the belt, elbowing him in the stomach as she did so. He saw her hand reach for the bag of chips and lunged, catching her around the waist and pulling her back into him.

"I'll do this."

She blinked at him, confused. He tried to smile but it came out as more of a grimace which just made her stare at him more. He leaned down and kissed her softly, running his fingers gently down her sides.

"Go. I can unload the cart. Better yet, wait in the car, take a break."

Casey looked dazed by his sudden change in behaviour but nodded slowly, reaching for Susie and hoisting her up on her hip.

"I'll go stand over there." She pointed to the far wall by the door and he nodded, swallowing as he watched her turn around. Quickly he slapped the condoms and chips on the counter.

"Ooh, extra large and strawberry. My favourite." Hannah winked at him as she rang the items up. Casey's head whipped around as she peered at him incredulously.

_Shit. This was not good._

It was even worse when they argued about it the whole drive home, and then, as soon as they got inside and handed Susie off to George, her first question was "What are condoms, Daddy?"

_Day Five, Tuesday_

Family movie nights were something Derek had avoided as a teenager. And he tried to avoid them now, even asking his step-mom if he could do the dishes.

But now, as he was sitting in the middle of the couch with Lizzie on his right, Casey on his left and Marti sitting on the floor, leaning against his legs, all three of them gasping and making retarded cooing noises at the same exact times...well, he would take a pile of dirty plates any day.

He sighed, at the same time as Edwin who was perched in his recliner and after quite a long argument with Marti finally telling both of them that if they didn't sort it out in the next five seconds, _she_ would take the seat...well, they sorted it quickly when Casey grabbed his arm, her nails digging in, and dragged him down into the spot beside her.

They had all decided on _Finding Nemo, _or Susie did when she threw her toy rattle at George when he suggested _Shrek._

Derek crossed his arms over his chest, elbowing Casey in the process, which made him smirk and her scowl.

"Fish are friends, not food."

Susie cracked up and everyone else laughed along with her. Derek closed his eyes and tilted his head against the back of the couch, blissfully allowing the soothing sounds of his family's laughter to nudge him off into sleep.

"Didn't you just love it Derek? I think I like it better now that I'm older." Marti was chatting away in his ear and he opened his eyes slowly to see her beaming face in front of his.

"You fell asleep."

Derek stifled a yawn with the back of his hand, blearily looking at the clock on the TV. 10:48pm. Way too early to be tired on a week day, especially during a vacation. The rest of the family had pretty much cleared out of the room.

Edwin was sitting at the dining room table, munching on a bowl of cereal as he flipped through an old videogame magazine that was probably taken from the box in the attic marked "Derek's Stuff. Keep Out!"

Nora was cleaning something up in the kitchen, and Derek smiled at the image. It was always hard for him to think of his Mom, his actual Mom, doing things like that. Cleaning, tidying up, and sending everyone else off to bed. He wasn't sure if it was because she never had done it, or he was actually too small to remember or appreciate it.

A hand with bright yellow and purple painted finger nails was waved in front of his face.

"Hello? Smerek? Earth to Smerek?"

"I'm here, Smarti."

She scoffed, and the image of Casey flashed in Derek's mind. He really needed to sleep.

"Barely. You look like you haven't slept properly in days, Derek."

_Four days, actually. _

"Nah, I'm fine."

_Liar._

But Marti didn't even need to hear him say the word; she just gave him a sad smile and clambered off his lap and on to the floor. "Go to sleep, Smerek."

With a sigh, Derek trudged off towards the basement, shooting a half hearted look up the stairs, where the rest of his family slept. Where Casey slept.

His feet stumbled on the stairs, and he grasped blindly for the railing, trying to regain his balance...and his hand collided with something soft and warm.

"Don't fall, D."

He exhaled, gasping for breath again quickly. It felt like forever since his lungs had done this. Breathed. Properly.

"Casey. What are you doing here?"

Her arm slipped around his shoulders as she led him down the stairs. "Mom washed the sheets on your bed today, and with her bad back, I told her not to worry about remaking your bed, I would do it. I was just in the middle of it too, when I heard you fall down the stairs."

"I did _not_ fall."

She gave him a small smile. "You just stumbled over a couple of steps?"

"Duh."

They reached the bottom now, and Derek blinked as they left the dark stairwell and entered the brightly lit, redone guest bedroom. It was actually pretty clean, except for the pile of wet clothes in the corner of the room from the water fight and the sheets and blankets bunched up on his bed.

"Grab the other corner." Casey said softly, moving to the one side of the bed, tucking the corners of the sheets in between the mattresses. He copied her actions, watching her.

"How are you?"

She snorted. "I'm fine, Derek. How are you?"

"Missing you."

She looked up from the sheets then, her eyes finding his. "I miss you too."

He finished tucking the sheet in, and crawled across the bed towards her. He pulled down and he lips met his half way.

God how he missed this.

He pulled her down into his half finished, messy bed grinning into the kisses. They hadn't done this since before they left, back in their apartment.

Casey sighed into the kiss, her fingers slipping into his hair as she pulled him closer to her, making the kiss deeper. Derek braced himself up on his arms on either side of her, pulling back to get a good look at her.

Casey's brown hair was fanned out on the pillow underneath her, lips pink and swollen and eyes that dark shade of blue that always made his brain slip up when forming sentences.

And as Casey began to pull him back down to her, he mumbled. "I told you I was the exception to all rules." Before fitting his lips firmly back over hers.

_Day Six, Wednesday_

The sunlight was filtering through the blinds hanging over his window and lighting the room in a way that was making his eyes want to fall closed again. It was relaxing and he felt content and he could breathe for the first time in...God, it's been a while since he's felt like this.

He rolled over onto his back, stretching his tangled limbs and glancing at his alarm clock on the nightstand. It was early. Way too early to be up on a Saturday and he felt himself sigh and slowly sink back into his pillow, letting sleep gradually descend upon him once again.

Until he heard a breathy _moan_ from somewhere to his left and _felt_ movement and hair _brush_ against his shoulder.

What the hell?

He breathed in deeply through his nose and squeezed his eyes shut. _What did he do last night?_

Oh right.

Casey.

He smirked a little and rolled over onto his side, so he was pressed up behind her. His arm slithered its way around her waist and his legs tightened around hers. Her hair was mused from sleep and last night's activities and he smiled when he felt her own hand come to rest on top of his, on her stomach.

He buried his face into her hair, breathing deeply and was so very close to letting those drowsy feelings overtake him when-

"Smerek?" Marti's voice called from upstairs.

He groaned and buried his face into Casey's long locks; eyes shut and prayed that he was back in his apartment with Casey and not in his bed back in his childhood home and he hadn't forgotten about his younger siblings just down the hall.

Casey stirred and he wrapped his arm tighter around her, pressing a soft kiss to her bare shoulder.

"Babe? It's time to get up now."

She made a tired noise, sort of like a yawn and a snort and shifted closer to him. He shook his head quickly; panic welling up in him as he heard his little sister's feet paddling down the steps with another set of feet following her.

_Oh God._

If it was Nora or his Dad...

They all knew about his and Casey's...relationship, which had started during their last vacation as a family at the lake and blossomed when they went to University. None of them were really upset about it, or disgusted. For the most part, they stayed in Kingston and came home every once and a while and kept the affections and touches at a minimum.

But now, they were here for a week and somehow, he didn't think Nora would be to happy to know Casey snuck out of Lizzie's room last night to come into his for sex.

He could hear his little sister at his door now, chatting away to whoever she was with. Her babbling woke him out of his stupor and he began to shake the drowsy brunette lounging next to him.

"Casey, you need to get up now." He hissed. There was a knock on his closed door and he shook her a little harder. "Like, now babe. You need to get up _now._"

"Derek?" His step-mothers voice asked, and he heard her try his locked door. "Are you up yet? Marti and I made chocolate chip pancakes."

She shook his door handles again, and he rolled his eyes. _It's not going to magically unlock now, Nora._

"Yeah just...just a minute!" He called back to her.

"Well, I'd hurry if I were you. Marti is getting the key."

He cursed his younger sister and her new found excitement for baking and chocolate.

"Casey? You need to wake up."

Casey made some sort of mumble and blearily opened her eyes.

"I'm trying to sleep, Der."

He rolled his eyes at the nickname he had told her, at least sixty four times, not to call him.

"Your Mother and Marti are going to come in soon, and unless you want them to see that how _close_ this relationship of ours is, I suggest you hide."

That woke her up a bit more, enough for her to sit up so she was eye level with him which didn't help his situation at all and his eyes slid from her face down to her uncovered chest.

"_Der-e_-!"

But that was all she could say because by then, he heard Marti scamper back to Nora, and the key being placed in the doorknob and he gave her the best apologizing look he could muster and pushed her off his bed.

The door opened and Marti dashed inside- a flurry of purple and flour- and launched herself onto his bed. He scrambled to grab the blanket around his waist and pull it tighter around himself. As long as Marti didn't insist on crawling under the covers with him, he was safe.

Nora followed more slowly and sat down on the corner of his bed. He could have sworn that he saw her glance to the other side of his bed, but he was probably just imagining things.

"Didn't you go to sleep with a shirt on last night, Derek?" Nora asked him.

Maybe not imagining things, exactly.

"Um...yeah, I did. But it was just getting so hot in my room; I had to lose a few layers."

Nora looked at him hard. Marti bounced on the bed beside him, oblivious to how tense the room had gotten. "You need to come and try these pancakes, Derek! I made one in a _Mickey Mouse_ shape just for you."

His eyes slid back to the eleven year olds face.

"Sounds great, Smarts. How about you go downstairs and get it all ready for me and I'll get dressed and meet you down there." He gave her convincing, innocent smile and she grinned back at him.

"Okay, Smerek!" She gave him a quick hug and hopped off his bed, dashing out of the room.

Nora sat there for a little while longer, staring at his face like she was trying to decipher some sort of cryptic code. He flashed her one of his smirks and she bristled, sitting up a little straighter.

"Wake Casey up for me please, I don't want to disturb her in case she's busy."

When his door finally closed and he was sitting alone on his head and could finally breathe again he leaned over the side of his bed to see Casey, wrapped up in his sheet, glaring up at him from the floor.

"If you ever push me off the bed again when we're not having sex, I will chop off certain parts of your anatomy and flush them down the toilet. Am I clear?"

He blinked.

"As crystal."

_Day Seven, Thursday_

The hugs, kisses and well wishes went by quickly and as Derek climbed into his car, watching Casey hug everyone one last time, he could have sworn he saw Nora whisper something to her that involved the word "strawberry".

Casey blushed and gave a stiff nod before turning around and getting into the passenger seat. I waited until we were away from the house, the street, the town of London before I asked her about what Nora has said.

She gave me a small smile. "Basically, she said that we're not that discreet."

I raised an eyebrow.

"We're loud." She clarified, her face flushed.

I turned, looking ahead. "Oh." It was quiet for a few moments before I remembered something and smirked. "So that's why I always get stopped by the old Mrs. Hamilton, who lives next door to us, asking me what that knocking noise is, at 2am."

Casey's face flushed an even brighter red and I laughed until she eventually joined in.

"Maybe next time," She said once they both calmed down, "I shouldn't make any of these rules, since they don't really work that well anyways."

Derek shot her a sideways glance. "Maybe, but I don't have any problems breaking rules with you. In fact, let's make a few more, add some dangerous, rebel tendencies to our relationship."

Casey laughed at him, smacking his shoulder lightly. "You are such a dork."

Derek pouted at his girlfriend. "That's it! The new rule is you have to keep your hands to yourself."

"That's ridiculous."

"Then why, Miss. Casey," Derek said, raising an eyebrow. "Don't you break that rule?" It was a challenge. And when he needed to pull over at a rest stop...for a few hours...well, let's just say that Casey took the challenge quiet seriously.


End file.
